Under United States copyright law, all appearances, names, similarities, etc, falls under FAIR USE as long as it is a parody. This means that if you simply change the name on the Launcher to something like: "Land of Fightcraft" and rename NPC's slightly so that they resemble what they once were, but different enough to justify that you are mocking it, then you can use it.

As a development team, you'd simply have to rename all the areas, NPC's, and so forth, as well as tweak the dialogue in the quests and record over some of the spoken dialogue in game to make yourselves impervious to further lawsuits as long as you credit everything to Blizzard and label it as a parody. It would not be an exact replica of what you were going for, but it would allow you to continue work on the project, and finish it after this lawsuit resolves.

Alternatively, under United States Copyright law, Fair Use also applies for purposes of criticism, commentary, news reporting, research, and scholarship (teaching).

The server could be saved by something as simple as an obligatory open disclaimer page similar to a terms of service page when you open the client, explaining in detail that the purpose of the Nostalrius server is to teach and educate a new decade of gamer how this rapidly evolving game began, and that this version of the game mimics the original incarnation of World of Warcraft down to the finest detail, replicated to the best of the scripting team's abilities as the original version of the code has been lost. The purpose of this server is not to undermine World of Warcraft in its current form, but rather teach a new decade of gamer how the game was back in 2005 and allow them to experience the drastic differences by reliving it rather than reading about it on a Wikia page.

A judge -has- to buy that. Not only is it the law, it's the only defense to the charges being filed against the server hosting company and Nostalrius development team. It also happens to be a particularly strong defense against this kind of thing, especially in this particular case where they've gone outside of U.S. Borders.

Here is an excerpt from an impartial observer Angus Morrison at PC Gamer:

"Nostalrius is a time capsule: a beautifully nostalgic record of what a living world used to look like. It's a museum piece created by passionate fans with no official alternative."

This review, to me, sounds very much like Mr. Morrison at PC Gamer acknowledged that the server was meant as an educational device to show the community what the game was like over a decade ago, when many of our players were too young to experience it in to its fullest. What other purpose does a time capsule, or a museum piece serve?

Furthermore, Nostalrius was a nonprofit organization, and while nonprofits require at least one person to be certified and for the organization to be registered as a nonprofit in the United States, I'm not entirely certain the same applies in France. Either way, a nonprofit organization is viewed in the eyes of United States copyright law as an educational institution.

In addition to this, it can be argued that the Nostalrius server had a transformative quality, in that much of the original code had to be re-written by a development team, making it so that the heart of the game was still gotten across, but many work hours had to go into making this a reality. All of these work hours were done for free and for noncommercial purposes.